This invention relates generally to antennas for electromagnetic communication between stationery locations along a roadway and vehicles traveling along the roadway equipped with transponders carrying information relating to the vehicle. In particular, this invention pertains to specific types of improvements in road mounted electromagnetic antennas configured to provide a predetermined signal field above the roadway surface providing reliable and accurate communication between the road antenna and the vehicular mounted transponder.
In our co-pending applications Ser. No. 446,231, filed on Dec. 5, 1989, a specific type of road antenna utilizing a collinear array was disclosed for use in establishing the proper radiation pattern providing a transponder capture zone above a roadway for communicating with a vehicular transponder. While the collinear design operates satisfactorily, applicants have discovered that a certain number of additional antenna designs can be utilized at or near the road surface in order to provide the necessary electromagnetic signal strength along the roadway thereby improving the transfer of information between the roadside station and moving vehicles. These improved antennas provide proper transponder capture zones which satisfy many installation difficulties.
In addition, certain of the antenna configurations disclosed in application Ser. No. 446231 disclosed may not be adequate in capturing the transponders of narrow vehicles such as motorcycles or motorbikes since these vehicles can operate near the edges of the lane or roadway and could deliberately or inadvertently avoid the signal produced by a conventional roadway antenna. The improved antennas disclosed herein include both the resonant standing wave, and non-resonant, i.e., travelling wave antennas including designs linear microstrip arrays, along with a slot antenna design.
It is therefore an object of this invention to provide a plurality of road mounted antennae having improved signal intensity patterns.
It is further an object of this invention to provide road mounted antennae suitable for capturing transponders carried by vehicles occupying reduced portions of a standard highway lane.
It is yet an additional object of this invention to improve antennas for road mounting which include reduced and/or simplified installation in the road surface.